Lubricants with improved biodegradability are desirable for example for equipment used in certain resource industries, such as forestry, mining, petroleum exploration and production, in particular wherever the lubricants themselves might come into contact with the environment.
Drilling fluids or muds are commonly circulated in the well during drilling operations in order to cool and lubricate the drilling apparatus, lift cuttings out of the wellbore and counterbalance the subterranean formation pressure encountered during drilling. An important function of a drilling fluid is to reduce the considerable torque on the rotating drill stem caused by the friction between the outside of the drill pipe comprising the drill stem and the wall of the well and/or casing strings. Drilling through offsets, deep wells and highly deviated or horizontal wells results in increased frictional forces, increasing the demand on the lubricating properties of the drilling fluids.
The oil and gas industry has used brines for well drilling and well completions for decades. High density brines have been found to be particular applicable for example in deep wells.
In particular during the operation of deep wells, as well as in extended reach and/or high angle wells, it is generally necessary for the brine-containing well treatment fluid to exhibit improved lubricity. The literature reports various additives for use as lubricating agents in drilling fluids as well as completion fluids, e.g. US 2010/016180 and DE 10 2005 060 459. Many of the reported additives are not, however, compatible with clear brines or drilling fluids or completion fluids which have brine as a major component. In addition, many additives used as lubricating agents in drilling fluids and/or completion fluids today have presented environmental concerns and tend to be costly.
Thus, a need exists for lubricating agents which may be used in brine-based drilling fluids and/or completion fluids. Such lubricating agents need to lower torque and drag by reducing metal to metal friction. Furthermore, they need to be useful in the prevention of differential sticking of downhole tubulars. Such lubricating agents further should be environmentally friendly.
It was therefore an object of the invention to provide a lubricant composition which is environmental friendly, is temperature and alkali stable and shows good solubility in brine based drilling fluids.